It is well known that the center of mass of a person completes vertical motions with each step when the person runs or walks. During each step the person lifts himself up for a few centimeters, spends certain energy, and loses the most portion thereof without return.
The main purpose of a typical footwear-supplementing device, which has an elastic system, is the conservation and returning the kinetic energy to the user and also the reduction of shock loads on the user's leg joints and spine.
The effectiveness of such a device depends on an optimal condition of the energy exchange between the device and the user in locomotion. This optimal condition exists when the inert forces are balanced with the elastic forces, which results in that the energy exchange between the user and the device is most efficient. This is known as a resonance phenomenon. However, the condition of resonance depends on each user's individual characteristics. If this device works well for one user, it does not necessarily mean that the device will work for another user as well. This is a serious disadvantage of such devices.
The instant invention is based on the concept that the design of a footwear-supplementing device has to consider the device itself and the user with his/her individual characteristics as a whole, i.e. as one common system. An individual setup or adjustment of the device needs to be applied to each user.
The known solutions do not usually take into consideration the aforementioned condition of resonance. Typical devices of this kind are taught, for example, in the following U.S. patents:
75,900Hale and Hubbell (1868)871,864Feazell and Thompson (1907)1,587,749Bierly (1926)4,360,978Simpkins (1982)4,534,124Schnell (1985)5,343,636Sabol (1994)However, the above-mentioned devices are not adjustable for a variety of users with different weight and manner of motion.
There is known a U.S. Pat. No. 6,436,012 issued to Naville (2002). Naville's device has an intermediate section composed of separate non-simple parts in order to adjust the resistance of the intermediate section according to the weight of a user. It however requires the availability of the parts for the intermediate section that increases the cost of the device. Besides, if these parts are metal springs, it will increase the weight of the device. Moreover, Naville's device is not adjustable to the manner of locomotion of a particular user. As a result, the user will have to adapt to the device, which is usually inconvenient. The opposite way is preferred, i.e. the device should be adjusted for the user.
There are also known U.S. Pat. No. 6,283,897 to Patton, U.S. Pat. No. 6,955,616 to Barth, and U.S. Pat. No. 7,736,285 to Brown. The elastic systems taught in those patents are based on elastomeric (e.g. ‘means for elastomeric tethering’ taught in Barth) or stretchable (e.g. ‘a first stretchable member’ and ‘a second stretchable member’ taught in Brown) members having a variable length (that create a resistance during exercises, e.g. ‘elastomeric resistance members such as surgical tubings’ taught in Patton), whereas the instant invention has no such stretchable members, but instead uses flexible members with a constant length that limit displacement of certain other device members.
Thus the mentioned related art devices have at least two problems:                1. The resonance phenomenon is not considered in the design and operation of the aforesaid devices. Therefore, those devices do not work optimally.        2. Every person has his/her unique condition of resonance. This condition is not addressed in the aforesaid devices.It should also be taking into consideration that the resonance condition causes difficulties in the development of a commercially viable footwear-supplementing device.        
The above indicated problems are partially solved in the aforesaid co-pending U.S. nonprovisional application Ser. No. 13/374,028 filed by the instant inventor. It provides an adjustable spring device for walking and running attachable to user's footwear, creating comfortable conditions during the locomotion. In embodiments, it includes: an upper lever and lower lever locating one above the other, wherein at least one of the levers is made of elastic material, and a support mechanism having a joint shaft that allows the levers to be pivoting. The device includes a first flexible link connecting the front ends of the levers, and a second flexible link connecting the rear ends of the levers. The links can be adjusted to a certain constant length before the deployment of the device. The device can be adapted by shifting the support mechanism between the levers and by adjusting the flexible links between the lever ends. However, the aforementioned device is complicated in manufacturing and use.